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Diversity of plasmids encoding histidine decarboxylase gene in Tetragenococcus spp. isolated from Japanese fish sauce

Masataka Satomi1, Manabu Furushita, Hiroshi Oikawa

  • 1National Research Institute of Fisheries Science, Fisheries Research Agency, Fukuura, Kanazawa-ku, Yokohama, Japan. msatomi@affrc.go.jp

International Journal of Food Microbiology
|May 28, 2011
PubMed

Insights

Histamine-producing bacteria in fish sauce carry plasmids with the histidine decarboxylase gene (hdcA). These plasmids, likely transferred via mobile elements rather than conjugation, contain diverse sequences, suggesting independent acquisition of the hdc cluster.

Area of Science:

  • Food Microbiology
  • Bacterial Genetics
  • Molecular Biology

Background:

  • Histamine accumulation in fish sauce poses a food safety risk.
  • Halophilic bacteria, particularly Tetragenococcus halophilus, are key histamine producers during fermentation.
  • Understanding the genetic basis of histamine production is crucial for controlling its levels.

Purpose of the Study:

  • To characterize the plasmids encoding the histidine decarboxylase gene (hdcA) in histamine-producing halophilic bacteria.
  • To investigate the genetic origin and dissemination mechanisms of the hdc cluster.
  • To analyze the genetic diversity of histamine-related plasmids in fish sauce isolates.

Main Methods:

  • Isolation and identification of histamine-producing bacteria from fish sauce mashes.
  • Phenotypic analysis and 16S rRNA gene sequencing for bacterial identification.
  • Polymerase Chain Reaction (PCR), Southern blotting, and complete plasmid sequencing.
  • Analysis of gene sequences, including adjacent regions and mobile genetic elements.

Main Results:

  • Nineteen histamine-producing halophilic bacterial isolates were identified as Tetragenococcus halophilus.
  • All isolates harbored 21-37 kbp plasmids containing the hdc cluster (four genes) responsible for histamine production.
  • The hdc clusters showed >99% sequence similarity, while other plasmid regions were diverse.
  • ISLP1-like and IS200-like mobile elements were found flanking the hdc cluster, suggesting a role in its transfer.

Conclusions:

  • The hdc cluster in Tetragenococcus plasmids is likely acquired via transformable elements, not clonal spread or plasmid conjugation.
  • The diversity of plasmid backbones suggests independent acquisition of the hdc cluster by different bacterial strains.
  • Mobile genetic elements play a significant role in the dissemination of histamine production genes in fish sauce bacteria.

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